In recent years, attention has been paid to using hydrogen as fuel because of no generation of global warming gas such as carbon dioxide in terms of the global environmental protection, and of the high energy efficiency. Particularly, attention has been paid to fuel cells because they can directly convert hydrogen to electric power and enable the high energy conversion efficiency in the cogeneration system utilizing generated heat. The fuel cells have been hitherto employed under the particular conditions such as in the space development and the ocean development. Recently, however, the development has advanced toward using them for automobile and household distributed power supplies, and fuel cells for portable devices have also been developed.
Among the fuel cells, the fuel cell for producing electricity by electrochemically reacting hydrogen gas obtained by reforming hydrocarbon fuel such as natural gas, gasoline, butane gas, or methanol, and oxygen in air is composed of a reformer for producing hydrogen gas by, in general, steam reforming hydrocarbon fuel, a fuel cell body for producing electricity, and so forth.
In the reformer for obtaining hydrogen gas by steam reforming methanol or the like as a feed material, a Cu—Zn catalyst is mainly used to carry out steam reforming of the feed material by an endothermic reaction. In the industrial fuel cell, since the startup and stop are not frequently carried out, a temperature fluctuation of the reformer is not liable to occur. However, in the fuel cell for automobile or portable device, since the startup and stop are carried out frequently, the reformer is required to rise up quickly (a time for reaching a steam reforming temperature of methanol is short) upon starting up from the stopped state.
On the other hand, particularly for the portable device, reduction in size of the fuel cell is essential so that reduction in size of the reformer has been studied variously. For example, there has been developed a microreactor having a silicon substrate or a ceramic substrate formed with a microchannel portion and carrying a catalyst in this microchannel portion (Laid-open Unexamined Patent Publication No. 2002-252014).
In the conventional microreactor, however, there has been a problem that the heat utilization efficiency is low so that the rising speed of the reformer is slow upon starting up from the stopped state. There has also been a problem that processing by a micromachine, etc. are required and therefore the production cost is high. Further, a space allowed for the microreactor is strictly limited in the fuel cell for portable device so that further reduction in size has been strongly demanded.
Further, the conventional microreactor has a low reaction efficiency and therefore a microreactor with a higher reaction efficiency has been demanded. Moreover, in the conventional microreactor, there has also been a problem that there is possibility of a catalyst to be deactivated by heat in the production stage, and therefore, a usable catalyst is limited and the production process management is difficult.
Furthermore, in the hydrogen production by the conventional microreactors, the microreactor is prepared for each of processes (mixing, reforming, CO removal) of the hydrogen production, and these plurality of microreactors are connected by piping, and therefore, a required space becomes large, which has seriously impeded the size reduction when a space allowed for the microreactors is strictly limited like in case of the fuel cell for portable device.
There has been a problem that when a catalyst is subjected to deactivation or degradation to lose its function in the microreactor for one process while being used, it is necessary to exchange the whole of the plurality of microreactors including the normally functioning microreactors, so that reduction in running cost is impeded.